The present invention relates to a method for the preparation of a lower alkyl ester of fatty acids or, more particularly, to a method for the preparation of a lower alkyl ester of fatty acids of high quality by the process of alcoholysis of a glyceride of fatty acids with a lower alcohol.
A lower alkyl ester of fatty acids such as methyl stearate is a useful industrial intermediate for the manufacture of soaps, higher alcohols, surface active agents and the like and is produced in a large quantity by the process of alcoholysis or transesterification of a glyceride of fatty acids with a lower alcohol such as methyl alcohol, ethyl alcohol and the like.
Since the glyceride of fatty acids used as the starting material in the above process is usually a naturally occurring oil or fat such as tallow or coconut oil, the lower alkyl ester products obtained therefrom unavoidably contain considerable amounts of colored or coloring impurities. Therefore, final products derived from the lower alkyl esters, such as soaps and higher alcohols, also have problems in the appearance and purity caused by the colored or coloring impurities contained in the intermediate material unless the intermediate material is used with further purification.
The impurities contained in the lower alkyl esters of fatty acids are known to belong to aldehyde compounds or phospholipid compounds of certain kinds and various attempts have been made to remove these impurity compounds from the product (see, for example, Japanese Pat. No. 53-114806).
The colored impurities contained in the lower alkyl esters of fatty acids are removed, in the prior art, by the method of rectification distillation, adsorption with activated clay or other adsorbents or treatment with an alkali. The former two methods are disadvantageous because the procedures are very complicated and troublesome in addition to the increased production costs by the reason of low yield of the desired products. The third method of alkali treatment utilizes a principle that, when a small amount of alkali such as sodium hydroxide is added as as aqueous solution into the reaction mixture of the alcoholysis reaction, the colored or coloring impurities are taken into the solution of the sodium salt of the fatty acids produced by the reaction of sodium hydroxide with the glyceride and separated from the product. This method also suffers from low economy due to low yields of the product.